Field of the Invention
The present invention generally relates to a signal transfer device.
Background Information
In general, the methods for transferring electrical signals are broadly grouped into two types: unbalanced transfer and balanced transfer. Unbalanced transfer is a method in which an electrical signal is transferred using a single transfer line. Balanced transfer is a method in which an electrical signal is converted into a pair of transfer signals of mutually opposite phase (differential signals), and are transferred using a pair of transfer lines, as in Japanese Laid-Open Patent Application Publication No. 2002-289992 (Patent Literature 1), for example.
A major difference between the two methods is the effect of noise received during transfer. For example, with unbalanced transfer, when the transfer line receives noise from the outside, the noise component ends up being superposed over the electrical signal being transferred. Accordingly, the effect of noise received from the outside cannot be avoided.
On the other hand, with balanced transfer, even if the pair of transfer lines receives noise, since noise signals of the same phase and same amplitude are usually superposed over the transfer signals, the noise components are removed when the two transfer signals are transformed into single-phase electrical signals. Therefore, the effect of noise received from the outside can be avoided. Accordingly, balanced transfer is usually used with a communication system that makes use of high-frequency signals, high-speed communication interface such as HDMI™ or LVDS (low voltage differential signaling). In the case of HDMI, the transfer line includes an inter-device HDMI cable or an intra-device HDMI signal line. Of these, some HDMI cables have good shielding and are resistant to noise, but inexpensive models may not be very resistant. Within a device, sometimes a common mode filter or the like is provided to an HDMI signal line, but even still quite a lot of noise is emitted. Also, it is often the case that when an HDMI signal line is close to another communication circuit, noise becomes admixed into the signals of the other communication circuit, and affects the characteristics of the other communication circuit.